Reducing the execution time of fair-queueing packet schedulers

Deficit Round Robin (DRR) is probably the most scalable fair-queueing packet scheduler. Unfortunately, it suffers from high delay and jitter with respect to a perfectly fair (and smooth) service. Schedulers providing much better service guarantees exist, but have a higher computational cost. In this paper we deal with this issue by proposing a modification scheme for reducing the amortized execution time of the latter, more accurate schedulers. Modified schedulers preserve guarantees close to the original ones, and can also handle seamlessly both leaves and internal nodes in a hierarchical setting. We also present Quick Fair Queueing Plus (QFQ+), a fast fair-queueing scheduler that we defined using this scheme, and that is now in mainline Linux. On one hand, QFQ+ guarantees near-optimal worst-case deviation with respect to a perfectly fair service. On the other hand, with QFQ+, the time and energy needed to process packets are close to those needed with DRR, and may be even lower than with DRR exactly in the scenarios where the better service properties of QFQ+ make a difference.